This invention relates to novel dispersible granule formulations of the herbicide oxyfluorfen and processes for their preparation.
Water dispersible granular pesticide formulations are known. These formulations are desirable because they avoid the use of potentially toxic solvents and permit the use of easily-disposable paper containers or water soluble containers. Potential exposure of pesticide applicators and the general public to the pesticide or solvent is thereby reduced.
Typical dispersible granular pesticide formulations are described for example in GB 1,433,882, EP 0,252,896 and U.S. Pat. No. 3,920,442. GB 1,433,882 describes a process for preparing dispersible granules by blending premilled, water-insoluble active ingredient, dispersing agents, disintegrating agents and wetting agents in an aqueous suspension. The aqueous mix is extruded to form granules which are then dried to yield the final product. U.S. Pat. No. 3,920,442 describes water dispersible pesticide aggregates containing 5 to 95% by weight of pesticide. The aggregates are prepared by contacting the finely divided solid ingredients in a fluidized bed with a fine spray of water or a solution of the binder-dispersant followed by drying.
In attempts at making pesticide granules, it has often been found that granules or agglomerates prepared from the formulated wettable powders of the art using well-known agglomerating techniques and using water as the agglomerating agent, are not easily dispersible in water. On the other hand, agglomerates which are readily water-dispersible are often not sufficiently resistant to attrition and form a fine dust fraction upon handling and shipping. If conventional binders are added to make the granules strong, then they are not dispersible in water. Techniques such as tabletting, extrusion and rolling which involve high-pressure compaction of moistened mixtures containing finely divided pesticides, diluents, binder and dispersant, as described in U.S. Pat. No. 3,617,246, lead to dense pellets, tablets, plates, and rods which are subsequently dried and crushed. These latter techniques have also been used to form granules containing up to 50% of active pesticide, but the resulting granules are not rapidly or completely water dispersible and are not suitable for use in preparing sprayable suspensions.
Low-melting solids such as oxyfluorfen present an especially difficult problem in the preparation of a dispersible granule formulation. The low-melting solid, herein defined as melting below 100.degree. C., tends to melt or become sticky during or subsequent to the grinding process which is a necessary step in preparing dispersible granules. EP 0,252,896 describes a possible solution to this problem which requires micro-encapsulation of low-melting pesticides prior to granulation. However, microencapsulation involves additional processing steps and adds to the cost of the overall formulation.
In the case of the herbicide oxyfluorfen, it has not heretofore been possible to produce a dispersible granular product which combines the features of a high active ingredient content, good suspensibility and dispersion properties as well as resistance to attrition thereby avoiding the formation of a dust.
Conventional oxyfluorfen formulations also suffer from the loss of herbicide vapor from the site of application which is undesirable because of reduction of herbicide in the soil and possible vapor injury to the growing crops in or near the location to which the herbicide is applied.
Oxyfluorfen is known to cause injury to soybeans by volatization under field conditions. Grabowski and Hopen, Weed Science 1985, Vol. 33, pg. 306-309 show that emulsifiable concentrate, wettable powder and soil applied granular formulations of oxyfluorfen cause vapor injury to plants under greenhouse conditions.